Adding Gum Arabic to your watercolour paints has three effects:
Gum Arabic slows down the drying time of the paint, giving you slightly longer to work on creating your image or working wet into wet
Gum Arabic adds further transparency to your watercolours and it increases gloss.
Gum Arabic washes will have greater depth and appear more luminous than colour washes alone.
Gum Arabic is usually mixed into the watercolour wash but can be added to the jar of water if you prefer to use it throughout the painting.
Gum Arabic should not be used directly from the bottle because thick films will be brittle.